1. Field of the Invention
The present invention relates to a shift-by-wire system and, more specifically, to a shift-by-wire system for shifting a drive condition of a vehicle transmission.
2. Description of the Related Art
In recent years, the tendency toward a transition from a mechanical driving system to an electrical driving system has grown in the field of vehicles such as automobiles in order to cope with a demand for space saving or improvement in assembling efficiency or controllability. As an example, development of a shift-by-wire system that uses an electric motor to electrically control range selection or switching, which can also be referred to as drive selection or switching, gear selection or switching, or the like, of an automatic transmission has been under way.
One shift-by-wire system that uses a by-wire control circuit unit to control the rotation of an electric motor to comply with a shift command inputted by a user and to thereby switch ranges has been disclosed in JP-A-2004-23890. Specifically, the system described in JP-A-2004-23890 designates a target rotational position so as to realize a target range to comply with the shift command, rotates the electric motor to the target rotational position, and thus achieves range switching. Moreover, when another shift command is inputted during switching control of ranges to comply with the shift command, the system in JP-A-2004-23890 designates a new target rotational position to comply with the re-shift command. Thus, the responsiveness to a shift command is improved.
In the system in JP-A-2004-23890, if a need arises for reversing the rotation of the electric motor due to a re-shift command inputted during a range switching control that is underway, the electric motor is rotated toward a new target rotational position only after the electric motor is suspended at the current actual rotational position. As a result, a range to be realized after the suspension of the rotation of the electric motor varies depending on the input timing of the re-shift command. However, difficulties may arise in that the realized range may cause the state of the automatic transmission to contradict an intended shift operation leading to a sense of discrepancy or discomposure to a user and creating a possibility of unintended shift operation-related consequences.